1. Technical Field
The present disclosure relates in general to systems and methods useful in the marine hydrocarbon exploration, production, well drilling, well completion, well intervention, and containment and disposal fields.
2. Background Art
Free-standing riser (FSR) systems have been used during production and completion operations. For a review, please see Hatton et al., “Recent Developments in Free Standing Riser Technology”, 3rd Workshop on Subsea Pipelines, Dec. 3-4, 2002, Rio de Janeiro, Brazil. See also U.S. Pat. No. 7,434,624. For other examples of FSR systems, see U.S. Published Patent App. Nos. 20070044972 and 2008022358, which disclose FSR systems and methods of installing same. Other patents mentioning further features of riser systems are U.S. Pat. Nos. 4,234,047, 4,646,840, 4,762,180, 6,082,391 and 6,321,844.
“Riser base gas lift” is a technique for improving production flow, especially heavy oil flow, in FSR systems. Szucs et al., “Heavy Oil Gas Lift Using the COR”, SPE 97749 (2005) discloses a riser base gas lift application using a concentric offset riser (COR).
American Petroleum Institute (API) Recommended Practice 2RD, (API-RP-2RD, First Edition June 1998), “Design of Risers for Floating Production Systems (FPSs) and Tension-Leg Platforms (TLPs)” is a standard in the subsea oil and gas production industry. Nitrogen is noted as a possible insulation medium for pipe-in-pipe risers in Bai et al., Subsea Engineering Handbook, page 437, (published December 2010), but only in the gap or annulus between the exterior surface of the outer riser and material insulation.
Webb et al., “Dual Activities Without the Second Derrick—A Success Story”, SPE 112869 (2008) mentions riser annulus dewatering using nitrogen, and discloses a spar platform having a surface nitrogen supply rig and a permanent nitrogen line for annulus dewatering using nitrogen. Assignee's U.S. non-provisional patent application Ser. No. 12/082,742, filed Apr. 14, 2008 (Ballard et al) describes using nitrogen to remediate hydrate plugs in hydrocarbon production systems.
While use of free-standing riser systems and methods of installation have increased, there remains a need for more robust designs, particularly when flow assurance is a concern as during a containment and disposal period, and for designs which can handle large amounts of potentially hydrate-forming gas, both during normal production operation and during containment periods. The systems and methods of the present disclosure are directed to these needs.